Rewrite DownloadsApiTest in C++.

chrome/browser/download/download_extension_api.h

Index: chrome/browser/download/download_extension_api.h
diff --git a/chrome/browser/download/download_extension_api.h b/chrome/browser/download/download_extension_api.h
index 9cf95f4f7dfdef600c59268c3480b20cfbe4638a..0eb303b25e98fe89a42cadf41a1f52c1a4f991b9 100644
--- a/chrome/browser/download/download_extension_api.h
+++ b/chrome/browser/download/download_extension_api.h
@@ -43,7 +43,7 @@ extern const char kInvalidOperationError[];
 extern const char kInvalidOrderByError[];
 extern const char kInvalidQueryLimit[];
 extern const char kInvalidStateError[];
-extern const char kInvalidUrlError[];
+extern const char kInvalidURLError[];
 extern const char kNotImplementedError[];
 
 }  // namespace download_extension_errors
@@ -357,6 +357,12 @@ class ExtensionDownloadsEventRouter : public content::DownloadManager::Observer,
   virtual void OnDownloadUpdated(content::DownloadItem* download) OVERRIDE;
   virtual void OnDownloadOpened(content::DownloadItem* download) OVERRIDE;
 
+  // Used for testing.
+  struct DownloadsNotificationSource {
+    std::string event_name;
+    Profile* profile;
+  };
+
  private:
   struct OnChangedStat {
     OnChangedStat();